Then, Officer Jay Young said, he flipped on a light switch and saw a young man kneeling over a reclining young woman; the male had one hand under the female’s Halloween costume skirt.

Young testified Tuesday in the trial of Miami student Yuyang David Bai, 20, in Butler County Common Pleas Court.

Bai, of Naperville, Ill., is accused of gross sexual imposition against an 18-year-old girl who prosecutors say was intoxicated. Bai also is accused of assault on a police officer and aggravated robbery for an alleged grab at Young’s gun during a scuffle.

But the student’s lawyer says the alleged sexual assault never happened – and that his client didn’t know that the young woman was drunk and he also didn’t know the person he tried to push past was a police officer. Attorney Wayne Staton said he doubts whether the victim was drunk, despite police arresting her earlier that night for underage consumption.

Young, however, testified that the young woman seemed “highly intoxicated” when he checked on her after Bai fled the scene. Other officers arrested Bai after Young radioed that the suspect had run away.

Under cross-examination, Young admitted he didn’t believe he announced he was a police officer before the suspect fought with him.

But Young showed the jury his official duty jacket he wore that night, which bears an embroidered badge on the chest and police department patches on the sleeves. Young also testified he used his police radio to try to alert dispatchers about what was happening.

At one point in the struggle, Young says he felt a tug on his gun belt, signifying that Bai was trying to grab his weapon.

Staton tried to get the officer to recount blow-by-blow what happened during the struggle, including whether the grabbing was on his belt or on his holster, until Judge Michael Sage urged Staton to cover new subjects in his questioning.

Young said he was unsure how long the fight lasted – possibly only a few minutes.

“It seemed like forever at the time, but I suspect it wasn’t very long. It was intense,” Young said.

Assistant Prosecutor Jason Phillabaum said Bai and the young woman had been strangers until that night. They met when Bai saw her outside her dorm building. A bus had dropped her off there after she was examined at McCullough-Hyde Memorial Hospital for underage intoxication.

The young woman was frustrated that she was unable to find a card that allows access to the building.

Bai lived in an adjacent building. He spotted her looking upset, Staton said, and tried to help her.

Staton said the young woman voluntarily walked with his client to the student center, where they shared ice cream and kisses. Staton asserts Bai never tried to take advantage of the young woman, and thought she wanted to be with him because she told Bai she liked him and he was cute.

Staton said his client simply panicked when Young encountered him in Gaskill Hall because Bai had been drinking while underage and knew he was inside a building without permission after hours.

The young woman is expected to testify when the trial resumes Wednesday.